1. Field of the Invention
The present invention relates generally to printing systems and more particularly to a system that generates data to be printed by a plurality of printing cartridges.
2. Description of the Background of the Invention
Composition programs such as QuarkXpress™ and Adobe InDesign™ enable a document designer to specify the content that is to appear on one or more pages of a document. Thereafter, the composition program generates a representation of the pages of the document in accordance with a page description language (PDL) such as PostScript or Portable Document Format (PDF) developed by Adobe Systems, Inc., or Printer Command Language (PCL) developed by Hewlett Packard, Inc. A raster image processor (RIP) generates a raster image representation of each page of the document from the PDL representation. The raster image representation may be used by a platemaker to create plates that are used on lithographic presses, an engraver to create engraved cylinders for a gravure press, or by a controller to drive the print units in a digital press. The raster image representation may be bitmap representation (one bit per pixel), a grayscale representation, or a color representation.
If a document incorporates variable data then the designer uses the composition program to create a template that specifies content of the fixed portion of the document (i.e., those portions that are not variable) and information regarding the position and content of the variable data areas. The designer may use a composition program that is specialized for creating the template. Alternately, the designer may use a composition program like InDesign or QuarkXPress with a plug-in or an XTension (a type of plug-in that works with by QuarkXPress) that allows the specification of information regarding variable data areas of a document. An example of a composition system that may be used to create templates is described in Warmus et al., U.S. Pat. No. 6,327,599, that is incorporated herein by reference. A data system combines information from a database with the template to generate PDL representations of the pages that represent the renditions of the variable data documents. The PDL representations may be in PostScript or PDF as described above or in formats (languages) designed to facilitate representation of renditions of variable data documents such as PPML, PPML/VDX, VPS, etc. The PDL representation may also be in page description languages based on PostScript or PDF that extend such formats through additional operators or libraries.
A RIP uses the PDL representation of the pages generated by the data system to create raster image representations of the pages for printing on a digital press. Such raster image representations are sent to one or more controllers in the press. The press controllers use the raster image representations to control printing by the press. The digital press may use any of number of printing technologies including electrophotography, ion deposition, magnetography, or ink jet.
Some printing systems use a printing unit that is capable of printing an raster image representation that is the width of a substrate supported by the printing system. However, the cost and complexity of such printing units increases as the width of the raster image representation printed thereby. To overcome this problem, printing systems have been developed where a first and a second printing unit are arranged such that the first printing unit prints a first swath of a first raster image representation and the second printing unit prints a second swath of a second raster image representation, wherein the first swath is printed adjacent to the second swath. In this fashion, a printing system have use two printing units, wherein each printing unit is able to print a 12 inch wide swath of a raster image representation, to print on a substrate that is 24 inches wide. Similarly, a printing system may use more than two printing units arranged in this manner to print on even wider substrates.
A RIP is associated with each printing unit of the printing system in which multiple print units are arranged to achieve a print width wider than the print width of an individual printing unit. Each RIP generates a raster image representation that is as wide as the printing unit associated therewith. Furthermore, typical RIPS operate on page boundaries. If a page is to be printed on the region of the substrate where a swath printed by a first printing unit abuts a swath printed by the second printing unit, the page must be composed using the composition system as two sub-pages. In particular, a first sub-page is composed that contains the information to be printed by the first printing unit and a second sub-page is composed that contains information to be printed by the second printing unit. Separate PDL representations are created for each of the first and second sub-pages, which are sent to the RIPs associated with first printing unit and the second printing unit, respectively. If a content element (e.g., an image or a text box) spans the boundary between the first sub-page and the second sub-page, the content element must be split into two sub-elements, wherein the first sub-element is part of the first sub-page and the second sub-element is part of the second sub-page. The splitting of the page and, possibly, the components thereof requires operator skill or additional features in composition tools. In addition, once a page is split into two sub-pages, the resulting sub-pages are bound to a particular type of printing system that is defines dimensions of the sub-pages. If the page is split in accordance with the characteristics of a first printing system and then needs to be printed on a second printing system (e.g., one with printing units that have a different print width), the page may have to be split again into sub-pages in accordance with the second printing system. For these reasons, it is difficult to use existing composition systems and RIP's to a generate raster image representation of a page that spans multiple printing units of a printing press.